1. Field of the Invention
The present disclosure relates generally to the treatment of respiratory and cardiovascular conditions, and more particularly, to methods and systems for indicating mask fit status in mechanical ventilation, such as continuous positive airway pressure (CPAP) therapy.
2. Description of the Related Art
Mechanical ventilators comprise medical devices that either perform or supplement breathing for patients. Early ventilators, such as the “iron lung,” created negative pressure around the patient's chest to cause a flow of ambient air through the patient's nose and/or mouth into the lungs. However, the vast majority of contemporary ventilators instead use positive pressure to deliver gas to the patient's lungs via a patient circuit between the ventilator and the patient. The patient circuit typically consists of one or two large bore tubes (e.g., 22 mm inner diameter for adults; 15 mm inner diameter for pediatrics) that interface to the ventilator on one end and a patient mask on the other end.
Ventilators may support either a single limb or a dual limb patient circuit. Single limb patient circuits are typically utilized for less acute clinical requirements such as the treatment of obstructive sleep apnea or respiratory insufficiency. In further detail, the single limb patient circuit, as its nomenclature suggests, involves gas flow from the ventilator to the patient and patient mask over a single conduit. The patient inspires fresh gas from the patient circuit, and expires carbon dioxide-enriched gas that is purged from the system through vent holes in the mask or exhalation ports in the tubing.
One particular application of ventilator devices is in the treatment of obstructive sleep apnea (OSA) syndrome, where the patient's upper airway narrows or collapses during sleep. There are repetitive pauses in breathing that may extend in duration up to half a minute. Although some degree of apnea is considered normal, in more severe cases, daytime sleepiness and fatigue may result as a consequence of reduced blood oxygen saturation, as well as constant interruptions to sleep cycles. In order to retain the patient's airway and ensure normal, uninterrupted breathing during sleep, continuous positive airway pressure (CPAP) therapy may be prescribed.
Generally, CPAP involves the application of positive pressure to open the patient's airway to prevent its collapse, as would otherwise occur during apnea. In a basic implementation, CPAP therapy applies a constant pressure that is not tied to the patient's normal breathing cycle. The positive airway pressure is desired in the inspiratory phase when the pressure differences between the lungs and the nose contribute to the collapse of the intermediate airway. Various improvements have been developed that reduce positive pressure flow to the patient during the expiratory phase, thereby reducing resistance to the patient's breathing efforts and patient discomfort. Further refinements that recognize the minimal flow and pressure toward the end of the patient's expiratory phase and responsively reduce the delivery of positive pressure have also been contemplated.
Typically, CPAP ventilator devices are comprised of a blower unit and a patient mask that are connected to each other over a gas flow conduit. The blower unit delivers the appropriate level of therapeutic gas flow to the patient as initially set by the clinician, and is further regulated based upon a function of the patient's breathing cycle. In order to maintain this gas flow, leakage from within the patient circuit, i.e., the pneumatic circuit comprised of the blower unit, the conduit, the patient mask, and the patient airway, must be maintained within acceptable minimum and maximum threshold levels. It will be recognized that if there little to no leakage, it may be indicative of the mask being placed on the patient too tightly, leading to discomfort and potential skin irritation. On the other hand, if there is too much leakage, the increased flow of gas may cause airway dryness, and cause airflow to be directed toward the eyes to cause dry eyes, and result in additional noise, all contributing to further patient discomfort. Furthermore, the leak may divert too much of the airflow to maintain the prescribed amount of positive pressure in the patient airway.
As a result of the need for increased gas flow, power consumption would increase. From a broader, environmental consciousness standpoint, increased power consumption is problematic, particularly for an apparatus that is run every day for approximately eight hours at a time, indefinitely. Seemingly minor instantaneous power surges over a single breathing cycle may each add up to substantial increases in overall power draw. Unnecessary power consumption is particularly problematic where the power source is limited, such as in battery-powered units.
In general, existing CPAP apparatuses regulate the delivery of therapeutic gas to the patient based upon flow volume measurements and/or calculations. With the flow value being available as a result thereof, leak indication may simply involve the display of those flow values, or the display of calculated percentages of flow values. The patient or the clinician therefore becomes responsible for evaluating the leakage status without additional meaningful assistance.
Accordingly, there is a need in the art for improved methods and systems for mechanical ventilation mask fit status indication, particularly in apparatuses utilized in continuous positive airway pressure (CPAP) therapy with dual pressure sensors at a source and on a ventilation mask. Furthermore, there is a need in the art for improved user interfaces for mask fit status indication.